84 Fertilizers 



sulfuric acid, making a superphosphate (monocalcic), and 

 a sulfate of lime or gypsum. That is, in this process, two 

 of the three parts of the lime combined with the phosphoric 

 acid to form the insoluble phosphoric acid, are removed, 

 thus leaving one part of the lime combined with the phos- 

 phoric acid, making the superphosphate. A pure super- 

 phosphate is, therefore, a mixture of soluble phosphate 

 and of sulfate of lime or gypsum. 



The difference in the superphosphates made from the different 

 materials. 



In the early use of superphosphates, the chief raw mate- 

 rial was animal bone. The superiority of the bone super- 

 phosphate, or dissolved bone, as it was called, over the raw 

 bone was manifest at once, and the familiarity with genu- 

 ine bone superphosphates thus early acquired by farmers 

 was, perhaps, quite as influential as any other in creating 

 a prejudice in favor of their continued use in preference to 

 superphosphates derived from mineral phosphates. The 

 opinion that the bone superphosphate is "the best" 

 is held even at the present day, notwithstanding the equally 

 satisfactory results that have been obtained from the use 

 of the superphosphates from other sources. 



Soluble phosphoric acid chemically identical, from whatever 

 source derived. 



Chemically speaking, the soluble phosphoric acid pro- 

 duced by the action of sulfuric acid upon mineral phosphates 

 is identical with the soluble phosphoric acid derived from 

 animal bone, and if the soluble from each could be separated 

 from the other substances with which they are associated, 

 there would be no difference whatever in the results of 

 their use. They are identical; just as much so as am- 



